Processes for the catalytic oligomerization of ethylene are well known. It has been shown that these processes produce even numbered carbon olefins having 4 to 50 carbon atoms and terminal double bonds. The preferred olefins are linear alpha olefins with 12 to 18 carbons numbers which are useful in detergents.
The catalysts employed for oligomerization are generally Ziegler-Natta or non-Ziegler type. The non-Ziegler catalysts include organonickel (0) compounds in combination with a modifier such as substituted 2,4-pentanedione as disclosed in U.S. Pat. No. 3,644,564 and employed in the Shell Higher Olefins Process (SHOP).
Ziegler type catalysts employ an alkyl aluminum or its derivative in combination with halides of titanium, zirconium or their complexes. Linear alpha olefins, C.sub.4 -C.sub.20 + having average molecular weight 70-300 and 90-100% purity are prepared by ethylene oligomerization in the presence of TiCl.sub.4 -RAlCl.sub.2 (A. Langer, J. Macromolelcular Sci. Chem., A4 (1970) 775).
French Pat. No. 266,992 describes the production of C.sub.4 -C.sub.10 alpha olefins in presence of Zr(OBu).sub.4 -THF-Et.sub.3 Al. Better control over distribution of alpha olefins is obtained using aryloxide of titanium modified by alkyaluminum sesquihalide as described in Indian Patent Application No. 526/Bom/94 now Indian Patent Application No. 182153 and European Pat. Appln. No. 95300318.3 (1995) (EP 0722 922) ZrCl.sub.4 -Et.sub.3 Al.sub.2 Cl.sub.3 -thiols reported in European Patents 241,596 and 481,435 produced a mixture containing C.sub.4 to C.sub.30 linear alpha olefins and high molecular weight polymers at higher pressures of ethylene.
However, all the prior art processes known to the applicants for oligomerization of ethylene suffer from certain drawbacks such as low degree of selectivity, formation of undesirable polymer low degree of conversion, etc.
Accordingly, it is a primary object of the present invention to provide a process for the oligomerization of ethylene to linear alpha olefins with a higher degree of conversion and selectivity.
It is a further object of the present invention to oligomerize ethylene to linear alpha olefins having 4 to 36 carbon atoms, preferably, with terminal double bonds, in a greater yield.
It is a further object of the present invention to provide a process for converting ethylene to relatively higher proportion of C.sub.12 -C.sub.18 linear alpha olefins.
Finally it is another object of the present invention to minimize the formation of undesirable high molecular weight polymers.